Add __hash__ for a bunch of types that set it to None (#13286)

stdlib/email/header.pyi

@@ -1,6 +1,6 @@
 from collections.abc import Iterable
 from email.charset import Charset
-from typing import Any
+from typing import Any, ClassVar
 
 __all__ = ["Header", "decode_header", "make_header"]
 
@@ -16,6 +16,7 @@ class Header:
     ) -> None: ...
     def append(self, s: bytes | bytearray | str, charset: Charset | str | None = None, errors: str = "strict") -> None: ...
     def encode(self, splitchars: str = ";, \t", maxlinelen: int | None = None, linesep: str = "\n") -> str: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     def __eq__(self, other: object) -> bool: ...
     def __ne__(self, value: object, /) -> bool: ...